Bonnie cuts a towering figure

Satellite radar shows mountainous
cloud chimney

Sept. 2, 1998:(this is the
thirteenth in a series of stories covering the ongoing CAMEX
mission to hunt hurricane data in a way not done since the 50s.
Other stories are linked in below.)

Tropical storm (now hurricane) Earl is seen Wednesday
morning in a composite view at right produced by the NOAA-12
polar-orbit weather satellite. The cooler clouds are white and
the warmer clouds are yellow. This image was produced by the
Ocean Remote Sensing Group at the Applied Physics Laboratory,
The Johns Hopkins University, Laurel, Md. (Links to

Hurricane Bonnie cut a towering figure
twice as tall as Mount Everest a week ago when it was scanned
by the first spaceborne rain radar as a part of a multi-level
field campaign. On Saturday, Aug. 22, the radar on the Tropical
Rainfall Measuring Mission (TRMM) observed a chimney of clouds
as Bonnie slowed and gathered strength north of Hispaniola and
east of the Bahamas.

The chimney formation was not observed by the Convection and
Moisture Experiment (CAMEX-3) science team - their crews were
resting and planning in anticipation of two days of eye wall
penetration flights - but a similar effect was observed on Aug.
25 when a dome-shaped cloud formed and snowed on the DC-8 Airborne
Laboratory.

The CAMEX-3 team made four sets of flights in front of, through,
and over Bonnie - several in coordination with TRMM overflights
- in the most extensive study of a hurricane ever. The team has
also made two sets of flights in and around Hurricane Danielle.
Future flight plans are under review. The team plans to fly a
TEFLUN (Texas and Florida Underflight) mission today. TEFLUN
is a separate campaign, to validate TRMM data, which complements
CAMEX-3's objectives. Today's flight by the DC-8, ER-2, and UND
Citation will be in the heavy stratiform rain region between
Panama City, Fla., and Tampa, Fla. Earl is heading for the U.S.
Gulf coast between Pascagoula, Miss. and Cameron, La.. A hurricane
watch is in effect from High Island, Texas, to Destin, Fla.

Meanwhile, Bonnie, which is churning the North Atlantic far
away from the CAMEX-3 study area, continues to surprise scientists
as they review data collected from the large array of instruments
used to studying the storm.

Although the GOES-8 weather satellite was watching Bonnie
the whole time, it was looking almost straight down on the storm
and could not see the interior structure. Thus, the grandeur
of the cloud chimney was difficult to appreciate - except for
TRMM's radar.

These compelling images depict a cumulonimbus
storm cloud, towering like a skyscraper, 18 km (59,000 ft) into
the sky from the eye wall of Hurricane Bonnie (shown at right
in a B&W GOES-8 image on the same day). (Note: The height
in these images is exaggerated for clarity. Colors correspond
to temperatures from blue [warm] to red [cold]). By comparison,
the highest mountain in the world, Mt. Everest, is 9 km (29,000
ft) and the average commercial jet flies at barely one-half the
height of the Bonnie's cloud tops. Scientists believe that towering
cloud structures like this are probably precursors to hurricane
intensification. This was the situation with Bonnie whose central
pressure dropped from 977 to 957 millibars in the subsequent
24 hours. These images were obtained on Saturday, Aug. 22, 1998,
by the world's first spaceborne rain radar aboard the Tropical
Rainfall Measuring Mission (TRMM), a joint U.S.-Japanese mission.
Each frame links to a 720x540-pixel JPG, 240 to 290KB in size).
Credit: NASA/Goddard Space Flight Center.

"It looks like a skyscraper in the clouds," said
Dr. Christian Kummerow, TRMM Project Scientist at NASA's Goddard
Space Flight Center in Greenbelt, Md. "This is the first
time that TRMM's precipitation radar has seen a structure of
this type in a hurricane approaching the U.S. East coast."

"Clouds this tall are rarely observed in the core of
Atlantic hurricanes," said Dr. Bob Simpson, former director
of the National Hurricane Center in Miami and the National Hurricane
Research Project. "This huge cloud probably happened because,
at the time the data was collected, Bonnie was moving very slowly.
The lack of movement kept funneling warm moist air into the upper
atmosphere, thus raising the entire height of the tropopause,
which is normally at around 45-52,000 feet (13.7-15.9 km).

The tropopause marks the upper limits of Earth's densest layer
of atmosphere, the troposphere, the layer starting at the surface
where we live.

"The vast amount of warm, moist air being raised high
into the atmosphere, and the subsequent release of latent energy
as this tropical air mass condensed into rain drops, is thought
to be the precursor of hurricane intensification, which was observed
in Bonnie in the 24 to 48 hours after these data were collected,"
Simpson continued.

This sequence of images depicts the eye and surrounding
structure Hurricane Danielle as they were seen by the Advanced
Microwave Precipitation Radiometer (AMPR) board the ER-2 aircraft
flying about 20 km above the clouds. At right is a color image
from the SeaWIFS instrument aboard the SeaStar satellite (links
to

). AMPR allows scientists to study storm convection and
intensity and eye wall structures, and to map rain how its absorbs
the Earth's own microwave radiation. The four strips in each
image depict the hurricane in 10.7, 19.35, 37.1, and 85.5 gigahertz
radio frequencies. Each image links to an 800x800-pixel, 93KB
to 101KB GIF showing how the storm appeared as the ER-2 flew
over the eye on different compass headings.

Many scientists believe that towering cloud structures, such
as the one observed by TRMM, are probably a precursor to hurricane
intensification. This was the situation with Bonnie, whose central
pressure dropped from 977 to 957 millibars in the subsequent
24 hours. Lower air pressure is associated with higher wind speeds
and overall storm strengthening.

Where do hurricanes get their wallop? A big part
of the answer is seen in this image built up from sea-surface
temperature measurements taken by the NOAA-K polar-orbit weather
satellite. The temperatures (warmer from blue to yellow to orange;
key is on the enlarged map) is derived from data taken Aug. 22-24
while Bonnie was nearly stationary. The line and color circles
track Bonnie's movement and growth during Aug. 21-29 as it gained
strength from the warm Atlantic off the Bahamas, then weakened
when it hit land, and never fully recovered as it moved into
the North Atlantic. This image was produced by the Ocean Remote
Sensing Group at the Applied Physics Laboratory, The Johns Hopkins
University, Laurel, Md. (Links to

"TRMM has flown over 100 tropical cyclones since its
launch in November of 1997," said Kummerow. "This enormously
enhances our database of cloud structures within tropical storms
during their growth and decay phases. It also greatly improves
the more restricted observations we have obtained from aircraft
radar and allows for the systematic study of this hurricane behavior
which appears to precede their intensification."

As the height of the hurricane season approaches, TRMM scientists
are looking forward to the continuing analysis of Atlantic hurricanes.

TRMM, launched Nov. 27, 1997, is the first dedicated to measuring
tropical and subtropical rainfall through microwave and visible
infrared sensors, including the first spaceborne rain radar.
TRMM fills an enormous void in the ability to measure world-wide
precipitation because so little of the planet is covered by ground-based
radars. Presently, only 2 percent of the area covered by TRMM
is covered by ground-based radars or surface rain gauges. By
studying rainfall regionally and globally, and the difference
in ocean and land-based storms, TRMM is providing scientists
the most detailed information to date on the processes of these
powerful storms, leading to new insights on how they affect global
climate patterns.

Note: More details are available in the NASA press
release describing CAMEX-3. Check back as hurricane season
progresses. We will post science updates as the campaign develops.

PIX: High resolution scans of 35mm camera photos from
the CAMEX-3 campaign are available from Public Affairs Office
at NASA headquarters. Please call the NASA Headquarters Photo
Department at 202-358-1900, or contact Bill Ingalls at bingalls@hq.nasa.gov.

CAMEX-3 - the third Convection and Moisture
Experiment - is an interagency project to measure hurricane dynamics
at high altitude, a method never employed before over Atlantic
storms. From this, scientists hope to understand better how hurricanes
are powered and to improve the tools they use to predict hurricane
intensity.

An overview
story (Aug. 12, 1998) describes
the program in detail. The study is part of NASA's Earth Science
enterprise to better understand the total Earth system and the
effects of natural and human-induced changes on the global environment.
A midterm story (Aug. 31, 1998) reviews the first month of
operations and the windfall of data.

Measuring distance and speed:
Because meteorology and aeronautics first used modified nautical
charts, their data bases are in nautical miles and knots (nautical
miles per hour). In these stories, we use Standard International
("metric") units first, and give more familiar measurements
in English units and the original measurements in nautical units.
Because of rounding and because the wind speeds originally are
expressed in knots, km/h speeds to knots may be slightly different
from the numbers in the story.

The Public
Use of Remote Sensing Data at Goddard Space Flight Center
has high-resolution images of Fran (including the original of
the image used in this story), Andrew, and other hurricanes and
of other events seen from space.